Wednesday, October 21, 2015

Triconodont and Multituberculate Mammals Found in Lower Cretaceous Japan

New mammalian specimens from the Lower Cretaceous Kitadani Formation, Tetori Group, Fukui, Japan


Miyata et al


New specimens of two non-therian (non-tribosphenidan) mammals are described from the Lower Cretaceous Kitadani Formation in the upper part of the Tetori Group, Katsuyama, Fukui Prefecture, Japan. Despite their poor preservation, these specimens represent undescribed species from Japan, suggesting additional mammalian diversity in the Tetori Group. Previously, four mammal taxa had been formally described from this rock unit: a spalacotheriid ‘symmetrodont’, two eobaatarid multituberculates and a eutriconodont mammal. One of the new specimens is a damaged left p4 of a ‘plagiaulacidan’ grade multituberculate assignable to the family Eobaataridae. The Kitadani eobaatarid is a large species distinguished from the two previously described eobaatarids, Tedoribaatar and Hakusanobaatar, which are known from the stratigraphically lower Kuwajima Formation of the Tetori Group, Hakusan, Ishikawa Prefecture, Japan. It also differs from Sinobaatar, Heishanobaatar and Liaobaatar described from the Early Cretaceous of China. Another specimen, a partial right dentary with a faint Meckelian groove, is assigned to a eutriconodontan that is larger than and morphologically distinguishable from the eutriconodont Hakusanodon from the Kuwajima Formation. The Kitadani eutriconodontan is potentially related to the family Triconodontidae. The additional specimens from the Kitadani Formation shed new light on Early Cretaceous mammalian faunal change and dispersal in East Asia.

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